The present invention relates in general to combination locks, and more particularly to combination locks having means incorporated therein for resisting surreptitious entry techniques of manipulation of the lock by unauthorized persons.
Conventional locks of the class known as combination locks usually comprise three tumbler wheels which are loosely journalled in coaxial, side-by-side spaced relation for rotation within a lock casing on a tubular arbor or tumbler post projecting inwardly from the front wall of the casing. The lock dial, which usually has one hundred peripheral calibration marks thereon, is affixed to a dial spindle which extends through the bore of the tumbler post and has keyed to the inner end thereof a disc-like drive cam which is likewise arranged coaxially with and spaced rearwardly from the tumbler wheels. A drive pin projects forwardly from the drive cam and has a lost motion connection through a conventional fly with the rearmost tumbler wheel to drive the tumbler wheel in selected relation to the drive cam. A similar lost motion connection is provided between each of the successive tumbler wheels so that each of the tumbler wheels may be driven upon predetermined rotation of the drive cam. Each of the tumbler wheels and the drive cam is provided with a peripheral notch or gate at a selected radial position on the drive cam and tumbler wheels.
A fence lever which is pivotally connected near one end to a reciprocative bolt slidably supported in the lock casing is provided with a depending nose near the opposite end which is designed to ride upon the drive cam periphery, in conventional combination locks, and has a bar or fence projecting laterally from the fence lever in overlying relation with the peripheries of the tumbler wheels. The position of the fence in relation to the length of the fence lever nose is usually such that the fence is spaced slightly from the peripheries of the tumbler wheels when the fence lever nose is riding on the drive cam periphery.
In such a conventional combination lock construction, when the tumbler wheel gates are out of registry with the fence and the dial is turned to the proper position to dispose the drive cam gate below the fence lever nose, the fence lever nose will drop slightly into the drive cam gate until the fence bears upon the tumbler peripheries. Rotation of the dial through small arcs in opposite directions from this position will bring the opposite surfaces of the drive cam gate into contact with the fence lever nose. The points at which the fence lever nose contacts these opposite surfaces at the entrance to the drive cam gate are known as the left and right contact points of the fence lever and may be detected by coordination of the senses of touch and sight by the person manipulating the dial. A variation in the angular distance between and "feel" of these contact points occurs when one of the tumbler gates is positioned beneath the fence, which is distinguishable from the angular distance between and "feel" of these contact points when all of the tumbler gates are out of registry with the fence. Because of the fact that the drive cam can be rotated through a sufficient arc when the fence is in contact with the tumbler peripheries to reveal the contact points of the fence lever nose, the location of the three tumbler wheel gates can frequently be determined by unauthorized persons by following a well-known lock manipulation procedure. Various modifications in combination locks structure have heretofore been resorted to to defeat detection of the lock combination in this manner. Among these is the lock structure disclosed in prior U.S. Pat. Nos. 2,575,674 and 2,807,954 granted to Harry C. Miller, wherein a guard or shielding slide is mounted on the rear face of the drive cam and has curved end portion conforming to the curvature of the drive cam periphery which normally overlaps the drive cam gate and forms a smooth continuation of the drive cam periphery to support the fence lever nose when the drive cam gate is in registry with the fence lever nose. An inner spindle extends through the dial spindle and is coupled at its inner end to the shielding slide at its outer end to a knob which is in exposed condition, whereby upon rotation of the knob and inner spindle, the slide may be shifted radially of the drive cam to expose the drive cam gate for reception of the fence lever nose. When the shielding slide is in projected position exposing the drive cam gate to entry of the fence lever nose, stop members on the lock casing are disposed in the path of movement of a portion of the slide to limit rotation of the drive cam to an extent which will prevent detection of contact points for the fence lever nose.
It has been determined, however, that the security of this lock may be adversely affected in time if the portion of the shielding slide which is projected beyond the drive cam periphery becomes worn, as by abrasion against adjacent surfaces of the lock casing. It is possible that the projected end surface of the shielding slide may become worn to a depth equal to the spacing of the fence from the tumbler wheel peripheries when the fence lever nose engages the driving cam periphery. In such a case, the slide may be only partially projected from the position wherein it shields the drive cam gate to lower the fence into contact with the tumbler peripheries and lower the fence lever nose into at least the entrance to the drive cam gate without projecting the slide sufficiently to permit the stop members to limit rotation of the drive cam. In this condition, the dial could be manipulated to permit sensing of the contact points and detection of the combination of the lock.
An object of the present invention, therefore, is the provision of a novel combination lock of the type having a mechanism which normally maintains the fence lever nose spaced out of contact with the driving cam periphery and the fence spaced out of contact with the tumbler wheel peripheries, and which may be operated to shift the fence lever into momentary engagement with the driving cam only when the driving cam is decoupled from the tumbler wheels to prevent surreptitious detection of the combination of the lock by unauthorized persons.
Another object of the present invention is the provision of a combination lock having over-center spring means which normally positions the fence and fence lever out of contact with the tumbler wheels and driving cam during manipulation of the driving cam to adjust the tumbler wheels to the positions determined by the combination of the lock, to prevent the feel and sound effects inherent in usual combination locks from assisting in unauthorized manipulation of the lock, wherein the over-center spring means is activated to shift the fence lever into coupled relation with the driving cam in a novel manner when the correct combination has been dialed.
Another object of the invention is the provision of a novel combination lock of the type described in the immediately preceding paragraph, wherein a spring activator device coupled to the fence lever normally maintains the fence lever in raised position out of contact with the driving cam and is activated momentarily by the driving cam in a special manner after the correct combination has been dialed to release stored energy to impel the fence lever and over-center spring means to shift the fence lever to unlocking position coupled with the driving cam.
Another object of the invention is the provision of a novel combination lock as described in the immediately preceding paragraph, including novel means for holding the fence and fence lever away from the tumbler wheels and driving cam and for releasing the spring activator to impel the fence toward the tumblers in response to shifting of the driving cam to an abnormal displaced position and for restoring the spring activator to a raised cocked condition by rotation of the driving cam.
Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating a preferred embodiment of the invention.